1. Field of the Invention
The present invention relates primarily to the field of aerospace and the field of lift generating structures. More specifically, the invention relates to the design of retractable rotor blades for a rotor blade assembly used to produce lift and thrust for vertical and short take off vehicles.
2. Description of the Related Art
Rotor blades have been used for many years to achieve flight. A shortcoming of the related art is that conventional rotor blades and rotor blade assemblies have longitudinally rigid structures (U.S. Pat. No. 7,475,847). Many rotor blades are now made of carbon fiber, fiber glass and other composite materials. These conventional composite rotor blades and composite rotor blade assemblies are manufactured to be used as rigid structures, not capable of being collapsed to a smaller volume (U.S. Pat. No. D 580,344). In order to be effective, conventional rotor blades often require very large rotor blade spans. Large rotor blades customary in VTOL (vertical take-off and landing) and STOL (short take-off and landing) vehicles typically require large storage space to house them.
In other examples of the related art, rotor blades are designed to reconfigure into a more stowable state (U.S. Pat. No. 6,176,679). This is often because they are to be housed indoors when not in use, or as an attempt to reduce the breadth of the rotor blade's slipstream when transported. Another example of the related art is the ability for some rotor blades to be capable of folding onto themselves (U.S. Pat. No. 4,086,025). Another example of the related art is the ability for some rotor blades to be retracted using a telescoping system (U.S. Pat. No. 6,972,498). The aforementioned example is made retractable by concentric telescoping solid rotor blade cross sections. A shortcoming of telescopically retracted systems is that they require each subsequent section of the rotor blade to be of a different dimension than the preceding one. This reduction of dimension and non-uniformity of the blade sections creates aerodynamic instabilities and it is not desirable.
Since the development of the airplane there have been many attempts to combine the ability of a flying vehicle with that of an automobile (U.S. Pat. No. 7,481,290). One particular example of such a vehicle has folding wings (U.S. Pat. No. 7,462,015). Another vehicle example requires the user to completely remove the lifting surfaces from the vehicle when being used as an automobile. Other examples of the related art incorporate road vehicles equipped with full scale aircraft wings. Other examples of the related art use rotor blades which fold upon themselves (U.S. Pat. No. 7,584,923). These designs are too cumbersome and do not provide the required compactability of the rotor blades to be used practically by road worthy vehicles. Some examples of the related art use fan blades to generate lift, but these require the fan blades to be operated at higher rpm. The requirement for higher rpm is due mainly to the small dimensions of the fan blades. Another example of the related art use fabrics as the exterior surface of the blade which is exposed to the airstream (U.S. Pat. No. 4,411,398).
Other objects and advantages of the present invention will become apparent from the following descriptions, taken in connection with the accompanying drawings, wherein, by way of illustration and example, embodiments of the present invention are disclosed.